Aminoazobenzene dyes

The PPP-MO method is suitable for the treatment of large molecules, does not present major computing demands and programs are now routinely used as a tool to calculate the colour properties of dyes. Unlike the HMO method, it handles heteroatomic species well. The method has been remarkably successful in calculating /lmax values for a wide range of dyes from virtually all of the chemical classes. For example, the method provides a reasonably accurate account of substituent effects in the range of aminoazobenzene dyes, including compounds 15a-f and 16a-f which have been discussed in terms of the valence-bond approach in the previous section of this chapter. 

Figure 7.7. Numerically, azo dyes form by far the most important chemical class of disperse dyes. Azo disperse dyes may be classified into four broad groupings. The most numerous are the aminoazobenzenes which provide important orange, red, violet and blue disperse dyes. They are exemplified by C. I. Disperse Orange 25 (157), C. I. Disperse Red 90 (158) and C. I. Disperse Blue 165 (159). A comparison of these three aminoazobenzene dyes provides an illustration of the bathochromic shift...

Figure 10.2 Orientation of an aminoazobenzene dye for maximum light absorption in a liquid crystal display...

Table 3.38 Light fastness of substituted aminoazobenzene dyes on nylon [175] and polyester [89,176]...

NORMALISED RELATIVE ADSORPTION POWER RATIOS FOR p-AMINOAZOBENZENE DYES ON >-AMINOAZOBENZENE IMPRINTED GELS ... 

Garg, A. Bhat, K. L. Bock, C. W. Mutagenicity of aminoazobenzene dyes and related structures a QSAR/QPAR investigation. Dyes Pigm. 2002, 55, 35-52. 

Macromolecular azo dyes which behave as photochromic polyelectrolytes have been reported where -aminoazobenzene dyes (VI and VII) are converted to the corresponding acrylamide and methacrylamide derivatives and are copolymerized with acrylic and methacrylic acids. 

Although several N-methyl-substituted arylamines have been shown to be carcinogenic (184-186), metabolic activation pathways have been investigated primarily for the hepatocarcinogenic aminoazo dyes, N-methyl-4-aminoazobenzene (MAB) and its 3 -methyl derivative (9,21, 22,187,188). N-Hydroxy-N-methyl arylamines are generally regarded as proximate carcinogenic metabolites (22,187,189) and have been shown to be converted to electrophilic N-sulfonyloxy derivatives by hepatic sulfotransferases (9,187) or to reactive N-arylnitrones by air oxidation (21). 

A striking feature of disperse dye development in recent decades has been the steady growth in bathochromic azo blue dyes to replace the tinctorially weaker and more costly anthraquinone blues. One approach is represented by heavily nuclei-substituted derivatives of N,N-disubstituted 4-aminoazobenzenes, in which electron donor groups (e.g. 2-acylamino-5-alkoxy) are introduced into the aniline coupler residue and acceptor groups (acetyl, cyano or nitro) into the 2,4,6-positions of the diazo component. A PPP-MO study of the mobility of substituent configurations in such systems demonstrated that coplanarity of the two aryl rings could only be maintained if at least one of the 2,6-substituents was cyano. Thus much commercial research effort was directed towards these more bathochromic o-cyano-substituted dyes. 

An interesting study of the relative rates of reduction of N,N-bis(2-chloroethyl)-aminoazobenzene and various monosubstituted derivatives (3.27) was initiated because of the ability of such dyes to inhibit the growth of animal tumours [23], even though some... 

The azo produets obtained have an extended conjugate system having both the aromatie rings joined through the -N=N- bond. These compormds are often coloured and are used as dyes. Benzene diazonium chloride reacts with phenol in which the phenol molecule at its para position is coupled with the diazonium salt to formp-hydroxyazobenzene. This type of reaction is known as coupling reaction. Similarly the reaction of diazonium salt with anUtne yields p-aminoazobenzene. This is an example of electrophilic substitution reaction. 

The most recent paper on this topic has been published by Lu and Huang (213). The method consists of an online enrichment of the aromatic amines on a carboxymethyl-bonded silica precolumn and an HPLC-UV (at 254 nm) analysis. The mobile phase, ACN-acetate buffer (pH 4.66) (40 60, v/v), was used to desorb the analytes and for the subsequent separation. The method was applied to the determination of several compounds (4-aminoazobenzene (4-AAB), benzidine (Bz), 3,3 -methylbenzidine (DMBz), 4-aminobiphenyl (4-ABP), 3,3 -dichlorobenzi-dine (DCBz), and 2-naphthylamine (2-NA) together with some substituted naphthalens and phenols) in aqueous solution of four food dyes Direct Blue 6, Amaranth, Sunset Yellow FCF, and D C Orange No. 4. Detection limits ranged between 0.6 and 1.6 fig/g. Most part of the methods developed for this kind of determination are reported in Table 3. 

In the 1940s and 1950s the pioneering studies of James and Elizabeth Miller provided early evidence for in vivo conversion of chemical carcinogens to reactive metabolites. They found that reactive metabolites of the aminoazo dye A, /V-dimcthyl-4-aminoazobenzene (DAB), a hepatocarcinogen in rats, would bind covalently to proteins and nucleic acids. The term, metabolic activation, was coined by the Millers to describe this process. Moreover they demonstrated that covalent binding of these chemicals was an essential part of the carcinogenic process. 

Stilbene dyes are in most cases mixtures of dyes of indeterminate constitution that are formed from the condensation of sulfonated nitroaromatic compounds in aqueous caustic alkali, either alone or with other aromatic compounds, typically arylamines [1], The sulfonated nitrostilbene (10) is the most important nitroaromatic, and the aminoazobenzenes are the most important arylamines. C.I. Direct Orange 34, 40215 [1325-54-8], the condensation product(s) of (10) and the ami-noazobenzene (11), is a typical stilbene dye. 

Disazo Dyes. About 10 % of all disperse dyes are disazo compounds [9], Even the simplest hydroxy disazo dyes, such as 4-aminoazobenzene coupled to phenol and 4-aminoazobenzene coupled to o-ere sol, have a good affinity for polyester fibers and yield lightfast reddish yellow hues. However, these shades are frequently less bright than those obtained with mono azo dyes. 

The simplest route to disazo dyes is by using / -am inoazobcnzcnc [60-9-3], As p-aminoazobenzene has been classified in the EU as carcinogenic, the use of derived disazo dyes like Disperse Red 151, DisperseYellow 7,Disperse Yellow23, and DisperseYellow56 has diminished. 

Examples From 4-aminoazobenzene-4 -sulfonic acid and benzoyl I-acid, the important red dye C. I. Direct Red 81,28160 [2610-11-9] (12) is obtained. 

A different way to synthesize a coupling component with two different basic groups is to treat A-dibromopropionylaminonaphtholsulfonic acids with dialkyl-amino alkylamines to give aziridine derivatives red dyes are obtained by coupling these with a diazonium salt of y>aminoazobenzene [83], e.g., 29. 

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